1. Field of the Invention
Hybrid DNA technology has already demonstrated the ability to produce products which heretofore were either not available or obtainable at extremely high cost and in relatively small amounts. Production of such proteins as human growth hormone, interferon, thymosin and others have already been announced as the forerunners of a large number of naturally occuring proteins as well as modified naturally occuring proteins which will have physiological effect. With the advent of the ability to make proteins, interest has arisen in expanding the type of product which can be produced, as well as the amount.
A number of situations would appear to put severe limitations on the efficiency, economics or ability to make a variety of products. Where a product is detrimental to the growth of the host microorganism, the cost of production of such products can become uneconomical. Similarly, in situations where the rate of production of a product of interest is off-set by the rate of its degradation, the yields may be uneconomically low. Also, where the product of interest is present in only an extremely small percentage of the total protein produced by the micro-organism host, so as to make isolation and purification a major problem, the economics may discourage development. Any one of these considerations can inhibit the production of a desired product and situations may be encountered whereby two or more of the above concerns may be combined.
It is therefore desirable to find new ways to produce products where previous experience has indicated that the products can only be difficultly produced, if at all, by microbiological techniques. Furthermore, there is continued interest in providing techniques which enhance the efficiency of production of products or allow for modulation of signals in a host cell to provide for the development of properties at will.
2. Description of the Prior Art
Uhlin, et al, Gene. 6 (1979) 91-106 describe plasmids with temperature-dependent copy number for amplification of cloned genes and their products. Bremer, et al, Molec. gen. Genet. 179, 13-20 (1980) describe production of a lethal product in a transformant from a structural gene on a plasmid. Bernard et al., Gene 5 (1979) 59-76 describes the use of a gene expressing a temperature-sensitive repressor controlling a lambda promoter coupled with structural genes. Heat induction is employed to regulate expression of the structural genes. Little, Molec. gen. Genet. 177, 13-22 (1979) describes production of a lethal protein product from a plasmid. Backman and Ptashne, Cell 13, 65-71 (1978) describe a strong promoter, namely the lac promoter. Hare and Sadler, Gene 3 (1978) 268-279 describe lac mutations resulting in enhanced repressor production.